Suppose we are on an ideal ship, sailing on perfectly smooth water without leaving a wake. We are not accelerating relative to the water. Can we do any experiment which will tell us whether or not our velocity relative to the water is nonzero?

Answers

1 Yes. We can toss a ball straight up. If it is deflected, we know we are in motion relative to the water.

2 No. The principle of relativity applies.

3 Yes. We can throw a stone into the water. If the ship moves with respect to the point from which the circular wavefronts emanate, then we are in motion relative to the water.

4 Yes. We can get a friend to fly over us in an airplane. If he sees we are moving, then we are in motion relative to the water.

none of the above